Cyclosporin A (CsA), a neutral cyclic undecapeptide isolated from the fungus Tolypocladium inflatum and currently marketed as Neoral® and Sandimmune® (Novartis, Basel, Switzerland), has been widely used for the prevention of organ transplant rejection. Cyclosporin A exerts its immunosuppressive effect at the molecular level by binding to the cyclophilin peptidyprolyl cis/trans isomerase. The resulting complex of cyclosporin A and cyclophilin binds to calcineurin, a Ca2+/calmodulin-dependent phosphatase, and inhibits its phosphatase activity. Calcineurin regulates the translocation of the transcription factor nuclear factor of activated T-cell (NFAT) and the subsequent expression of early genes necessary for T-cell proliferation. Inhibition of the phosphatase activity of calcineurin by the cyclosporin A-cyclophilin complex prevents NFAT nuclear localization and suppresses the expression of genes like IL-2, ultimately leading to immunosuppression (Matsuda et al., “Mechanisms of Action of Cyclosporin”, Immunopharmacology, 47:119-125 (2000)).
Cyclosporin A also has potential therapeutic application in the treatment of autoimmune diseases such as rheumatoid arthritis, Crohn's disease, psoriasis, and chronic inflammatory diseases, such as asthma. Unfortunately, clinical utility for these indications has not been realized because of the side effects such as nephrotoxicity, hypertension, hepatotoxicity, anaemia, and gastrointestinal intolerance that occur with clinically effective doses of cyclosporin A. The toxicity associated with cyclosporin A is believed by many experts working in the immunosuppression therapeutic area to be mechanism based (Lazarova et al., “Cyclosporin A Analogues: Recent Advances”, Expert Opin. Ther. Patents, 13:1327-1332 (2003)). Indeed, the goal of discovering novel cyclosporin analogues with improved therapeutic index has yet to be achieved despite the significant efforts in this drug discovery area over the last three decades (U.S. Pat. No. 5,525,590 to Bollinger et al.; U.S. Pat. No. 5,643,870 to Boelsterli et al.; U.S. Pat. No. 5,639,852 to Rich et al.; U.S. Pat. No. 5,236,899 to Durette; U.S. Pat. No. 5,122,511 to Patchett et al.; U.S. Pat. No. 4,914,188 to Dumont et al.; U.S. Pat. No. 4,771,122 to Seebach; U.S. Pat. No. 4,764,503 to Wenger; U.S. Pat. No. 4,396,542 to Wenger; U.S. Pat. No. 4,210,581 to Ruegger et al.).
More recent efforts to find novel cyclosporin analogues with potent immunosuppressive activity and decreased toxicity are underway and have led to compounds such as ISATX247. Preclinical observations indicate that ISATX247 has the potential to be significantly more potent and less toxic than other immunosuppressants in its class already available on the market for the prevention of transplant rejection. ISATX247 is in phase II clinical trials for the prevention of organ rejection after transplantation and for the treatment of psoriasis (Abel et al., “ISATX247: A Novel Calcineurin Inhibitor,” J. Heart Lung Transplant, 20:161 (2001); Aspeslet et al., “ISATX247: A Novel Calcineurin Inhibitor,” Transplantation Proceedings, 33:1048-1051 (2001); U.S. Pat. Nos. 6,605,593 and 6,613,739 to Naicker et al.).
A “soft” drug approach (Lazarova et al., “Synthesis and Biological Evaluation of Cyclosporin A Analogues: Potential Soft Drugs for the Treatment of Autoimmune Diseases,” J. Med. Chem., 46:674-676 (2003)) has also recently been described that seeks to minimize the toxicity of immunosuppressive cyclosporin A derivatives used for the treatment of autoimmune diseases (International Patent Publication No. WO 03/033010 to Or et al.) and respiratory diseases, such as asthma (International Patent Publication No. WO 02/069902 to Or et al.).
There is still a large need for novel cyclosporin analogues with improved therapeutic index.
The present invention is directed to achieving these objectives.